Electronics Devices and Circuit Theory - Chapter 2-boylestad

Electronics Devices and Circuit Theory - Chapter 2

1. Chapter 2:
Diode Applications

2. Load Load--Line Analysis Line Analysis
The load line plots all possible
combinations of diode current ( I
D)
and voltage (V
D) for a given circuit.
The maximum I
Dequals E/R, and
the maximum V
Dequals E.
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The point where the load line and
the characteristic curve intersect is
the Q-point, which identifies I
Dand
V
Dfor a particular diode in a given
circuit.

3. Series Diode Configurations Series Diode Configurations
Constants •
Silicon Diode: V
D= 0.7 V
•
Germanium Diode: V
D= 0.3 V
Analysis (for silicon)
Forward Bias Forward Bias
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•
V
D= 0.7 V (or V
D= Eif E< 0.7 V)
•
V
R= E – V
D
•
I
D= I
R= I
T= V
R/ R
33

4. Series Diode Configurations Series Diode Configurations
Diodes ideally behave as open circuits
Analysis
•
V
D= E
•
V
R
= 0 V
Reverse Bias Reverse Bias
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•
I
D= 0 A
44

5. Parallel Configurations Parallel Configurations
V
.7
V
10
D
V
E
V 9.3
R
V
V 0.7
O
V
D2
V
D1
V
V 0.7
D
V
−
−
=
= = =
=
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mA 14
2
mA 28
D2
I
D1
I
mA 28
.33k−
V
.7
V
10
R
D
V
E
R
I
= = =
=
−
=
−
=

6. Half Half--Wave Rectification Wave Rectification
The diode only
conducts when it is
forward biased,
therefore only half
of the AC cycle
passes through the
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passes through the diode to the
output.
The DC output voltage is 0.318V
m, where V
m= the peak AC voltage.

7. PIV (PRV) PIV (PRV)
Because the diode is only forward biased for one-half of the AC cycle, it is
also reverse biased for one-half cycle.
It is important that the reverse breakdown voltage rating of the diode be
high enough to withstand the peak, reverse-biasing AC voltage.
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PIV (or PRV) > V
m
•PIV = Peak inverse voltage
•PRV = Peak reverse voltage
•V
m= Peak AC voltage

8. Full Full--Wave Rectification Wave Rectification
The rectification process can be improved by
using a full-wave rectifier circuit.
Full-wave rectification produces a greater
DC output:
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•Half-wave: VV
dcdc= 0.318 = 0.318VV
mm
•Full-wave: VV
dcdc= 0.636 = 0.636VV
mm
DC output:

9. Full Full--Wave Rectification Wave Rectification
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Bridge Rectifier Bridge Rectifier
•
Four diodes are connected in a
bridge configuration
•
V
DC= 0.636V
m

10. Full Full--Wave Rectification Wave Rectification
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Center Center--Tapped Transformer Tapped Transformer
Rectifier Rectifier
Requires
•Two diodes
•Center-tapped transformer
V
DC= 0.636V
m

11. Summary of Rectifier Circuits Summary of Rectifier Circuits
Rectifier Rectifier Ideal Ideal VV
DCDCRealistic Realistic VV
DCDC
Half Wave RectifierV
DCDC= 0.318V
mV
DCDC= 0.318V
mm– 0.7
Bridge RectifierV
DCDC= 0.636V
mV
DCDC= 0.636V
m– 2(0.7 V)
Center
-
Tapped Transformer
V
= 0.636
V
V
= 0.636
V
–
0.7 V
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1111
V
m= peak of the AC voltage.
IIn the center tapped transformer rectifier circuit, t he peak AC voltage
is the transformer secondary voltage to the tap.
Center
-
Tapped Transformer
Rectifier
V
DCDC
= 0.636
V
m
V
DCDC
= 0.636
V
m
–
0.7 V

12. Diode Clippers Diode Clippers
•
The diode in a
series clipper series clipper
“clips”
any voltage that does not forward
bias it:
•
A reverse-biasing polarity
•
A forward-biasing polarity less than
0.7 V (for a silicon diode)
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13. Biased Clippers Biased Clippers
Adding a DC source in
series with the clipping
diode changes the
effective forward bias of
the diode.
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14. Parallel Clippers Parallel Clippers
The diode in a
parallel clipper parallel clipper
circuit “clips” any voltage that
forward bias it.
DC biasing can be added in
series with the diode to change
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series with the diode to change the clipping level.

15. Summary of Clipper Circuits Summary of Clipper Circuits
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more… more…

16. Summary of Clipper Circuits Summary of Clipper Circuits
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17. Clampers Clampers
A diode and capacitor can be
combined to “clamp” an AC
signal to a specific DC level.
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18. Biased Clamper Circuits Biased Clamper Circuits
The input signal can be any type
of waveform such as sine, square,
and triangle waves.
The DC source lets you adjust
the DC camping level.
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the DC camping level.

19. Summary of Clamper Circuits Summary of Clamper Circuits
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20. Zener Diodes Zener Diodes
The Zener is a diode operated
in reverse bias at the Zener
Voltage (V
z
).
•
When V
i
≥≥≥≥V
Z
–
The Zener is on
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2020
–
Voltage across the Zener is V
Z
–
Zener current: I
Z
= I
R
–I
RL
–
The Zener Power: P
Z
= V
Z
I
Z
•
When V
i
< V
Z
–
The Zener is off
–
The Zener acts as an open circuit

21. Zener Resistor Values Zener Resistor Values
ZK R L
I I I
−
=
min
min
max

L
Z
L
I
V
R=
If Ris too large, the Zener diode cannot conduct because the availab le amount of
current is less than the minimum current rating, I
ZK. The minimum current is
given by:
The maximumvalue of resistance is:
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Electronic Devices and Circuit Theory, 10/e
Robert L. Boylestad and Louis Nashelsky
2121
min
max
L
Z
L
L
L
R
V
R
V
I= =
Z i
Z
L
V V
RV
R
−
=
min
If Ris too small, the Zener current exceeds the maximum curre nt
rating, I
ZM . The maximum current for the circuit is given by:
The minimumvalue of resistance is:

22. Voltage Voltage--Multiplier Circuits Multiplier Circuits
•
Voltage Doubler
•
Voltage Tripler
•
Voltage Quadrupler
Voltage multiplier circuits use a combination of di odes and
capacitors to step up the output voltage of rectifi er circuits.
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2222

23. Voltage Doubler Voltage Doubler
This half
-
wave voltage doubler’s output can be calculated by:
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This half
-
wave voltage doubler’s output can be calculated by:
V
out
= V
C2
= 2V
m
where V
m
= peak secondary voltage of the transformer

24. Voltage Doubler Voltage Doubler
•Positive Half-Cycle
oD
1conducts
oD
2is switched off
oCapacitor C
1charges to V
m
•Negative Half-Cycle
oD
1is switched off
oD
2conducts
o
Capacitor C
charges to V
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o
Capacitor C
2
charges to V
m
V
out = V
C2= 2V
m

25. Voltage Tripler and Quadrupler Voltage Tripler and Quadrupler
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26. Practical Applications Practical Applications
•Rectifier Circuits
–
Conversions of AC to DC for DC operated circuits
–
Battery Charging Circuits
•Simple Diode Circuits
–
Protective Circuits against
–
Overcurrent
–
Polarity Reversal
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Electronic Devices and Circuit Theory, 10/e
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–
Polarity Reversal
–
Currents caused by an inductive kick in a relay circuit
•Zener Circuits
–
Overvoltage Protection
–
Setting Reference Voltages
2626